Originally Posted by Road Fan

I don't think the auto industry had it wrong. Auto standards, even when modernized, are burdened with history. Decades ago, auto headlights used lightbulbs which were probably (before my time) less than reliable. Then it moved to standard sealed beams, halogen bulbs, and halogen sealed beams, still less than stone-reliable or durable. Two lights were a necessity for the ability to drive after a single headlight or taillight failure. The driver was expected to get the car fixed promptly, but to be able to drive to a repair place.

Modern car headlights (HID or LED) are far more durable and reliable, so perhaps we're approaching the day when a single front light is adequate.

So the questions for a bike light are:

First, what are the functions and performance requirements for each function?
Can the functions be provided with a single front light? In other words, can a fixed light do everything, or is it necessary to have a helmet light as well?
Is the selected lighting technology reliable enough that you don't need redundancy?

For dyno-driven LEDs with quality cables and connectors and well-sealed electronics, probably redundancy isn't necessary, but if you think you also need a head-mount lamp for pointability, ... well, the fixed light can't provide that.

There are a lot of lighting functions and potential approaches to fulfilling them - for an entire bike, a single "best" system of lights that gives you all-year applicability, we have a pretty complicated engineering problem to solve.